The invention relates among others to the production of a front portion of a housing or for a housing of a writing instrument having a refilling device (refill), said front portion comprising a sleeve body made of a shape-retaining material (preform) and a jacket covering a surface of said sleeve body along a substantial part of a length thereof, said jacket being made of a material having elastic gripping properties. When said writing instrument is used, said jacket serves as a gripping zone which is adapted to give a good hold to a user""s fingers. For this purpose, the outer surface of said jacket can also have a conical extension. Said jacket can be adapted to have an elastic ductility appropriate to the purpose.
In writing instruments comprising a front part that, for a better handling, is mostly adapted to have a conical extension, sprue portions of elastic materials cause problems, since the material tears off uncontrolledly when being separated or detached from a mold. Therefore, efforts are made to hide said sprue portions. When hiding said sprue portions and when covering a front part of a writing instrument at an outside thereof from an inside and through walls thereof with a material that has elastic gripping properties, a conducting channel for a thermoplastic melt cannot be adapted to extend through a refill opening (refilling device opening or guiding and penetration opening), since said opening is adapted to usual refilling devices, thus having a diameter which is too small for sufficiently economically providing a guiding channel with cores. Therefore, it is necessary to adapt a front portion of a front part of a writing instrument to have a larger diameter for initially applying a circumferential jacket made of a material that has elastic gripping properties around said front portion, and for subsequently, in a further working step, applying a tip portion by ultrasonic welding or friction welding. Only then, said subsequently provided tip portion can be adapted to have a diameter at a front end thereof which is small enough to laterally support the refilling device.
Therefore, a one-piece sleeve body cannot be used, on the contrary, due to production processes, a two-piece sleeve body is inevitably required, said sleeve body comprising a first portion and a tip portion applied subsequently. An object of the invention is to reduce the cost for producing such front parts of writing instruments, and further to keep sprue portions of soft parts hidden, even if a one-piece sleeve body is used as a blank for receiving a portion which is applied circumferentially (said portion having elastic gripping properties).
In order to simplify production and to reduce production cost, the invention provides a penetration and guiding portion at the tip of a sleeve body (refill opening), said portion being adapted as a portion of an injection channel for a material of an outer jacket, said material having elastic gripping properties, at least partly circumferentially in a radially outward direction, without a metallic support of a ram-shaped core which is (relatively) moved into said sleeve body in front of a rear end thereof. Said core either starts only behind said channel segment of said blank, at or from a diameter allowing a practical application of a material conduct in said core, or has a channel conduct that is open towards an outside.
Said sleeve body has at least one aperture in a jacket portion thereof through which a material forming a gripping zone is conducted from an inside towards an outside, from said injection channel segment to an outer circumferential portion of said sleeve body. One of said penetration and guiding opening at said tip of said sleeve body and an adjoining portion of said inside of said sleeve body can be adapted as a portion enlarging towards said inside of said sleeve body or as a portion having an undercut.
Due to said properties and to the ability of injecting a material supplied as a second material, particularly a thermoplastic elastomer, by using a two-component injection molding technology through a refill opening provided in said sleeve body to a circumferentially limited extent, said sleeve body itself can be provided in one piecexe2x80x94without a weld or a connecting seamxe2x80x94, thereby substantially simplifying and accelerating the production of a front part of a writing instrument, and thus reducing production cost.
For obtaining a better attachment by complementary shapes between said jacket and said sleeve body, said sleeve body can be provided with at least two apertures distributed over a circumference thereof, said apertures being filled in when forming (injection molding) said surface-covering jacket. For improving said connection, at least one of said apertures can be provided with a contour enlarging from and outside towards an inside thereof; since there is no material bond between the two materials of said two-component injection molding technology (the materials do not stuck together), a better support of said circumferential jacket at saidxe2x80x94inside locatedxe2x80x94shape-retaining sleeve body is obtained by said mechanical arrangement, said support also having a surface effect.
A production in two-component injection molding technology comprises a first component for producing a shape-retaining sleeve body of a relatively brittle plastic material, such as ABS; a second component serves for producing a jacket and uses a thermoplastic elastomer (TPE). Initially, a shape-retaining sleeve-body is produced, said sleeve body comprising a penetration and guiding opening (for a refilling device inserted later) and at least one, preferably two apertures in a circumferential wall thereof. An elastomer forming an outer jacket is applied along a considerable lengthxe2x80x94a multiple of the diameter of said refill openingxe2x80x94of said circumferential wall, far into a tip portion, said elastomer being injected through a penetration and guiding opening of said sleeve body into an inner space thereof, particularly being contactingly supported and conducted, for being guided from said inner space through said aperture(s) towards an outside onto a circumferential wall of said sleeve body, and for being shaped on said circumferential wall to obtain a continuous circumferential jacket.
It is not disturbing that, after penetrating into the penetration and guiding opening inside said sleeve-body, the stream of said second material, when being injected, is initially enlarged in cross-section, said second material being only subsequently conducted to an outside through an aperture of said preform. During production, said penetration and guiding opening (refill opening), which has one of a cross-section enlarging towards an inside of said sleeve body and an undercut, is blocked by an inserted core as of an axial position, said position being located behind, particularly markedly behind a front end of said refill opening. Thus, said refill opening (tip opening) forms part of an xe2x80x9cinjection channelxe2x80x9d conducting a melt of said second material, and can therefore be small in diameterxe2x80x94corresponding to a refilling device inserted laterxe2x80x94without opposing a too high flow resistance to said injection process in a post pressure phase. Inserting a core extending to a front end for guiding said melt is dispensable.
A particular embodiment of a top portion of said core can result in said core still extending further into said tip portion, up to said refill opening, nevertheless maintaining the inventive idea. However, in said portion, no inside guiding channel of said core is required, said core having a metallic outside cover, on the contrary, at least one portion of a circumference (in case of laterally open channels) or the entire circumference (in case of a core having a conical top portion) of said inside surface of said sleeve body is used for closing the guiding channels left open by said top portion of the core. Said guiding channel can have an annular shape. A plurality of combinations are possible, starting from a shorter core not extending completely up to said refill opening, but leaving an axial length free. At least one wall piece of a guiding channel is provided forming an axially and circumferentially extending wall portion of a guiding channel, said guiding channel receiving the melt of said second material and conducting it to a respective aperture. A length of said respective wall piece is at least one half of a diameter of said refill opening, said length particularly being larger than said diameter of said refill opening.
Being located at an inside, the sprue portions (separating portions) of said jacket having elastic gripping properties are allowed to tear off uncontrolledly upon separating sprue channels, thus not disturbing the handling nor the outer appearance.
Said sleeve body can be embodied in one piece, even if a front opening thereof is adapted to a usual diameter of a refilling device, thus being too narrow for additionally receiving a core which, additionally, would have to comprise an inner channel for transporting a softened plastic material. By simultaneously using a short, but marked portion of said tip as a guiding channel segment (also xe2x80x9csprue channel segmentxe2x80x9d), it is ensured that no additional narrow portions occur in the entire flow channel, so that during the injection process, a post or dwell pressure phase can be effected without problems to compensate a shrinkage of said second material. Nevertheless, a second production step required by additionally attaching a conical tip portion is dispensable, which has a favorable effect on the production cost.
A further advantageous effect of the invention is that the gripping zone can extend further into said tip portion, since a subsequent attachment of a tip portion having a length of about 1.2 to 1.5 cm is not required. In principle, it would even be possible to approach said elastic gripping zone from outside substantially completely towards said refill opening, so that no visible blank of a more solid plastic material protrudes out of said gripping zone at a front end thereof any more.
Even a mold separation of a material thus injected which uses a refill opening predetermined by a diameter of a refilling device as a channel segment, is absolutely reliable, even if a usual sleeve body is provided with a refill opening having a shape enlarging towards an inside. If said material has elastic gripping properties, even in a solidified state, it can nevertheless be removed in an axially forward direction, the connection portions being located inside shearing or tearing off. Preferably, said connection portions can have a much thinner shape than the remaining channel portion, said connection portions nevertheless hardly having any influence on the dwell pressure phase since they have a very short length.
An additional improvement of said separation is obtained by correspondingly embodying the distribution channel pieces which are provided in a core such that they radially deflect said TPE melt supplied through said channel segment of said sleeve body. If they comprise cut edges or at least sharp upper edges, a cull or slug or sprue can easily be removed by a puller core, even if said refill opening comprises a conical portion in a cone being adapted to extend in an opposite direction with respect to a removal direction. Conical openings in a core are advantageous.
A sleeve body comprising a plurality of apertures distributed over a circumference thereof serves for attaching or fixing said jacket at a plurality of positions of said sleeve body, all apertures being filled in with said jacket material. However, said thermoplastic material needs to be conducted out of said injection channel of said sleeve body only through one ore two of said apertures, the remaining apertures being filled in from outside, from said jacket portion.
Inserting said core into said sleeve body has to be effected carefully, insofar as said sleeve body can be provided with a conical thread and can therefore easily be ejected from its support by axial forces when said shaping space has not yet been closed. In order to avoid this, said sleeve-shaped blank is initially moved into said shaping space, preferably by a pivoting movement, and received in its support, said core being inserted partly but not completely into said blank, preferably by about 80% to 90%. Thereupon, a molding or shaping plate is closed, said plate supporting an injection cavity, allowing said sleeve-shaped blank to be supported at a front end by a circular or an annular support line. Said blank having been supported, said core is completely inserted, without ejecting saidxe2x80x94now supportedxe2x80x94blank from its support.